Understanding HGH: Growth Hormone, IGF 1, and the Growth Hormone Axis

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Understanding HGH: Growth Hormone, IGF 1, and the Growth Hormone Axis​

Human Growth Hormone is one of the most recognizable hormones discussed in fitness and bodybuilding.

But despite the name, growth hormone does considerably more than simply influence physical growth.

It forms part of a complex endocrine network involving the hypothalamus, pituitary gland, liver, IGF 1 and numerous tissues throughout the body.

Understanding this system makes HGH much more interesting than simply viewing it as a performance related hormone.

What Is HGH?

HGH stands for Human Growth Hormone.

The naturally occurring hormone is also known as somatotropin.

Growth hormone is produced by specialized cells within the anterior pituitary gland.

Its secretion is controlled through signals involving the hypothalamus and several physiological feedback mechanisms.

Pharmaceutical forms of recombinant human growth hormone also exist and have established medical applications for specific diagnosed conditions.

The 100 IU designation sometimes seen with HGH products describes a labeled quantity expressed in International Units. It should not be interpreted as a recommendation for individual use.

Growth Hormone Is Released in Pulses

One of the most interesting characteristics of natural growth hormone is that it is not released at exactly the same rate throughout the entire day.

Secretion occurs in pulses.

These pulses can vary according to factors including sleep, age, nutrition, exercise and other physiological signals.

Significant growth hormone secretion is associated with periods of sleep, demonstrating one of the many connections between sleep and endocrine physiology.

This pulsatile pattern is important because a single measurement does not always provide a complete picture of someone's natural growth hormone secretion.

The Hypothalamus and Pituitary Gland

Growth hormone secretion begins with communication between the brain and pituitary gland.

The hypothalamus produces signals that can stimulate or inhibit growth hormone release.

The pituitary then responds by releasing growth hormone into circulation.

This forms part of a regulated endocrine system rather than growth hormone operating independently.

Feedback from downstream hormones and metabolic signals helps regulate the entire process.

What Is the Growth Hormone Receptor?

Once released into circulation, growth hormone can interact with growth hormone receptors located in different tissues.

Activation of these receptors initiates intracellular signaling.

Some effects of growth hormone occur directly through these pathways.

Other important effects occur indirectly through another hormone that frequently appears alongside HGH in bodybuilding discussions.

That hormone is IGF 1.

Understanding IGF 1

IGF 1 stands for Insulin Like Growth Factor 1.

Growth hormone can stimulate production of IGF 1, particularly in the liver, although IGF 1 is also produced locally within other tissues.

IGF 1 then interacts with its own receptor system.

This creates an important relationship between growth hormone signaling and growth factor signaling.

However, HGH and IGF 1 should not be treated as though they are the same hormone.

They are different signaling molecules with different receptors and biological roles.

The Growth Hormone and IGF 1 Axis

The relationship between growth hormone and IGF 1 is often described as the growth hormone IGF 1 axis.

This system contributes to normal growth and development as well as aspects of metabolism and tissue regulation.

Feedback mechanisms help prevent the system from operating without control.

This is a common theme throughout endocrinology.

Hormones rarely function alone.

Instead, they operate within networks where one signal can influence another and downstream hormones can feed information back to earlier stages of the pathway.

HGH and Metabolism

Growth hormone also participates in metabolic regulation.

Its effects can influence how the body handles fats, carbohydrates and other energy substrates.

This is one reason growth hormone discussions extend beyond childhood growth.

However, metabolic effects should always be considered as part of whole body physiology.

Changing one hormonal pathway can influence other systems, including glucose regulation.

HGH Has Legitimate Medical Applications

Recombinant human growth hormone has established medical uses.

These applications involve specific diagnosed conditions and medical supervision.

The existence of legitimate medical applications is important because it separates evidence based treatment of hormone deficiency or other approved conditions from nonmedical performance use.

More hormone is not automatically equivalent to better health or better physiological function.

Normal endocrine systems depend on balance and feedback.

HGH and IGF 1 LR3 Are Different

Since IGF 1 LR3 was discussed recently, this distinction is worth emphasizing.

HGH acts primarily through the growth hormone receptor and can stimulate natural IGF 1 production.

IGF 1 LR3 is a modified analogue related to IGF 1 and associated primarily with research.

The two should therefore not be treated as interchangeable compounds.

Understanding the receptor involved immediately makes the difference much clearer.

Why Sleep Deserves More Attention

The relationship between sleep and natural growth hormone secretion is particularly relevant to anyone interested in training.

Sleep is not simply passive downtime.

It is associated with important neurological, metabolic and endocrine processes.

This is one reason consistently improving sleep can sometimes contribute more to recovery than constantly searching for another supplement or increasingly complicated training strategy.

The Bigger Picture

HGH provides an excellent introduction to how endocrine systems communicate.

The important fundamentals are:

HGH means Human Growth Hormone.

Natural growth hormone is produced by the anterior pituitary gland.

Its secretion occurs in pulses.

Growth hormone interacts with growth hormone receptors.

It can stimulate production of IGF 1.

IGF 1 has its own receptor system and biological functions.

The growth hormone IGF 1 axis is regulated through multiple signals and feedback mechanisms.

Growth hormone also participates in metabolic regulation.

Recombinant growth hormone has legitimate medical applications for specific conditions.

Understanding these fundamentals gives a much clearer picture of HGH than simply associating it with growth or bodybuilding.

Which part of the growth hormone system would you like explored next: natural HGH pulses, the pituitary gland, IGF 1 signaling, or the relationship between sleep and growth hormone?